chore: add more comments

crates/rapier3d-urdf/README.md

@@ -0,0 +1,37 @@
+## STL loader for the Rapier physics engine
+
+Rapier is a set of 2D and 3D physics engines for games, animation, and robotics. The `rapier3d-urdf`
+crate lets you convert an URDF file into a set of rigid-bodies, colliders, and joints, for usage with the
+`rapier3d` physics engine.
+
+## Optional cargo features
+
+- `stl`: enables loading STL meshes referenced by the URDF file.
+
+## Limitations
+
+Are listed below some known limitations you might want to be aware of before picking this library. Contributions to
+improve
+these elements are very welcome!
+
+- Mesh file types other than `stl` are not supported yet. Contributions are welcome. You my check the `rapier3d-stl`
+  repository for an example of mesh loader.
+- When inserting joints as multibody joints, they will be reset to their neutral position (all coordinates = 0).
+- The following fields are currently ignored:
+    - `Joint::dynamics`
+    - `Joint::limit.effort` / `limit.velocity`
+    - `Joint::mimic`
+    - `Joint::safety_controller`
+
+## Resources and discussions
+
+- [Dimforge](https://dimforge.com): See all the open-source projects we are working on! Follow our announcements
+  on our [blog](https://www.dimforge.com/blog).
+- [User guide](https://www.rapier.rs/docs/): Learn to use Rapier in your project by reading the official User Guides.
+- [Discord](https://discord.gg/vt9DJSW): Come chat with us, get help, suggest features, on Discord!
+- [NPM packages](https://www.npmjs.com/search?q=%40dimforge): Check out our NPM packages for Rapier, if you need to
+  use it with JavaScript/Typescript.
+
+Please make sure to familiarize yourself with our [Code of Conduct](CODE_OF_CONDUCT.md)
+and our [Contribution Guidelines](CONTRIBUTING.md) before contributing or participating in
+discussions with the community.